1. Field of the Invention
This invention relates to reciprocating engines having crankshaft, connecting rods and piston rod units.
2. Description of the Prior Art
FR814987 and FR828306 disclose engines in which combustion take place at both sides of the piston. The difficulty of piston cooling, the lubricant loss and the bulk are some of the disadvantages of these engines.
Further disadvantage that renders them inferior to conventional engines is the restriction on the valve size and the valve location that the existence of the piston rod imposes. Taking into consideration that in the contemporary conventional engines the disadvantages of the L-head, F-head and T-head engines from the combustion chamber point of view, have rendered them obsolete, one can conclude that, whatever obliges the valve size or location to be restricted more than they are restricted in the conventional over-head valve engine, renders the engine inferior to the respective conventional engine due to the overwhelming effectiveness of the valve size and location over all the rest characteristics of a contemporary poppet valve engine. There is not substitute for the volumetric efficiency.
In double action pistons, the necessary cross section moment of inertia of the piston rod is given by the column loading theory to be J=(4/a.pi..sup.2)P.sub.c l.sup.2 /E, which for round rod yields: EQU d.sup.4 bP.sub.c l.sup.2 /E (1)
where b depends on the type of rod supporting; being for cantilever rod b=1.
According (1), the diameter of a round rod d is proportional to the root of its length l and inversely proportional to the fourth root of the modules of elasticity of the material and independent on the strength of the material. Actually the situation is worse, because it is the combined length of piston rod and connecting rod under column loading, at least on the crankshaft-cylinder axis plane.
Thus, any development in materials will be of no value for d and materials of low E, like Titanium alloys are of no utility, despite their high strength/weight ratio that makes them attractive for moving engine parts.
U.S. Pat. No. 5,167,208 shows an engine in which combustion takes place exclusively on that side of the piston facing the crankshaft. This engine, however uses a relatively large diameter piston rod which would limit the space available for the valves and thus limits the possible intake and exhaust gas flow. Here, it is the strong bending moment on the piston rod that imposes a rod of several times thicker than what is capable to cope with the axial forces alone.
Further disadvantage of the double acting piston is the dissimilarity of the two types of cylinders and combustion chambers that are formed at the two faces of the piston. They are not only geometrically different but they also have a considerable difference in the time available to each of them for the completion of its combustion, because the piston motion of a crank-connecting rod mechanism around top dead center is faster, by a factor (1+S/2L) times, than its motion around the bottom dead center, where S is the stroke and L is the connecting rod effective length. For instance, for L=2S the dwell at bottom dead center is 1.25 times longer than the dwell at the top dead center, namely the time available to the combustion chamber formed at the closer to the crankshaft end of the cylinder, to complete its combustion is 1.25 times more than the time available to the chamber formed at the remote from the crankshaft end of the cylinder and it may give a magnitude of the likely difference in efficiency and performance between the two sets of the different kind of chambers of the double action piston engine. Contemporary practice trends show that not only for diesel engines but also for spark ignition engines this difference, in the available time, is likely to have a considerable effect in their efficiencies and performances.